The present invention is generally directed to toner processes, and more specifically to processes for the preparation of encapsulated toner compositions. In one embodiment, the present invention is related to a process for the preparation of encapsulated toners comprised of a core and a shell, and wherein the process comprises mixing an olefinic monomer, a free radical initiator, a pigment, an optional charge control agent, and a polymer resin A soluble in the organic phase; dispersing this mixture in an aqueous medium containing a surfactant, and heating the resultant stabilized microdroplet to effect the free radical polymerization of the olefinic monomer to polymer resin B, wherein both resin A and B are incompatible and phase separate to form a shell and core morphology. In another embodiment, the present invention is related to a process for the preparation of encapsulated toners comprised of a mixture of an olefinic monomer, such as for example isobutyl methacrylate or styrene, a free radical initiator, a pigment, and optionally a charge control agent, and a condensation polymer resin A such as a polyester, a polyurea, a polyamide, or polyurethane soluble in the organic phase; dispersing this mixture in an aqueous medium containing a surfactant; and heating the resultant stabilized microdroplet to effect the olefinic polymerization of the olefinic monomer to resin B, yielding an encapsulated toner wherein the condensation polymer resin A and the polymer resin B phases are incompatible and separate such that a shell and core morphology is obtained. Accordingly, in one embodiment of this invention, the condensation polymer A phase separates to the surface of the microcapsule toner resulting in a condensation polymer shell, such as a polyester shell, and the core is comprised of the addition-type polymer resin B, such as poly(isobutyl methacrylate), pigment and optionally a charge control additive. In other embodiments, the addition-type polymer, such as the aforementioned poly(isobutyl methacrylate) resin B phase separates to the microcapsule surface, and the core is comprised of pigment, an optional charge control agent and the condensation polymer, such as a polyester. The primary advantages associated with the processes of the present invention in embodiments is that the condensation polymer resin is not formed by an interfacial polymerization as illustrated, for example, in U.S. Pat. Nos. 4,000,087 and 4,307,169, the disclosures of which are totally incorporated herein by reference. Thus, with the processes of the present invention there is avoided the use of undesirable toxic diacid chlorides, and diisocyanate monomers to form condensation polymers, and there is avoided the generation of byproducts associated with interfacial condensation polymerization such as inorganic salts or organic salts such as sodium chloride, hydrogen chloride alkylamino chlorides, and the like. Additionally, with the process of this invention, there are obtained encapsulated toners comprised of a core comprised of a condensation polymer such as a polyester, pigment and charge control, and comprised thereover a shell consisting of an addition-type polymer resin such as poly(isobutylmethacrylate) or polystyrene. The aforementioned polystyrene shell-polyester core, for example, cannot be readily obtained by known prior art processes, and the processes of the present invention are advantageous for obtaining excellent pigment dispersion of from about 70 to about 100 percent transmittance. Excellent pigment dispersion can be measured by fusing an image on transparency and acquiring the projection efficiency using a Match Scan II photospectrometer. Furthermore, with the process of this invention, encapsulated toners with low heat fusibility, excellent triboelectrification and admix, high projection efficiency, high gloss, nonblocking, nonghosting and nonsmearing properties are obtained.
It is known that encapsulated toners offer numerous advantages over conventional pulverization processes. The conventional pulverization process involves melt mixing of the toner ingredients such as a resin, pigment and charge control, followed by extrusion, grinding and energy consuming jetting process to obtain the desired volume average particle size of from about 7 microns to about 21 microns as measured by the Coulter Counter. Additionally, for the aforementioned particle size to remain unchanged until required for fixing on paper by reprographic methods, the glass transition temperature of the conventional toner should be not less than 50.degree. C., and preferably not less than 55.degree. C. after manufacturing, transporting or storage. This glass transition temperature of the toner can restrict the type of fuser rolls utilized in reprographic fixing systems and a fusing temperature of no less than 150.degree. C. and preferably no less than 160.degree. C. such that the toner can be fixed adequately onto paper. Encapsulated toner process enables, for example, the preparation of a core with a glass transition temperature of from about -70.degree. C. to about 50.degree. C. and surrounded by a shell material of glass transition temperature of above 50.degree. C. The primary function of the shell is to prevent toner agglomeration until used during the fixing step, at which time shell rupture by the application of pressure by the fusing roll is accomplished thereby releasing the core resin primarily responsible for sticking, fixing and adhering to the paper. Accordingly, one main advantage of encapsulated toners is that they can be fixed adequately onto paper at lower roll fusing temperatures, such as from about 100.degree. C. to about 130.degree. C., thereby reducing the energy consumption of the fuser as well as prolonging its lifetime. Additionally, encapsulated toner processes can offer other advantages over conventional processes, such as the ability to produce smaller size toner of less than 7 microns necessary for higher resolution in reprographic applications. Many prior art encapsulated toner compositions utilize condensation polymers as the shell component, such as a polyester or a polyurethane, which can be obtained by the interfacial condensation of diisocyanate or diacid chloride monomer with diols, amines, aminoethers and the like, and causing the generation of byproducts such as salts and hydrolyzed diacid chloride or diisocyanate monomers. The encapsulated toner processes of this invention do not utilize expensive and toxic reagents such as diisocyanates or diacid chlorides, and do not generate byproducts in embodiments. Additionally, with the process of this invention in embodiments there can be obtained encapsulated toners comprised of a core comprised of a condensation polymer of low glass transition of less than 50.degree. C., such as a polyester, pigment and charge control, and thereover a shell comprised of an addition-type polymer resin, such as poly(isobutylmethacrylate) or polystyrene, with a glass transition temperature of above 50.degree. C. not readily, if attainable with prior art processes.
Certain encapsulated toners and processes thereof are known. For example, both U.S. Pat. No. 4,626,489 and British Patent Publication 1,538,787 disclose similar processes for colored encapsulated toners wherein the core resins are prepared by free radical polymerization and the shell materials are prepared by interfacial polymerization. U.S. Pat. No. 4,565,764 discloses a colored microcapsule toner comprised of a colored core encapsulated by two resin shells with the inner shell having an affinity for both the core and the outer shell materials. Also mentioned primarily as background interest are U.S. Pat. Nos. 4,671,954; 4,644,030; 4,482,606 and 4,309,213. Disclosed in U.S. Pat. No. 4,636,451 is a process for the preparation of encapsulated toners wherein the shell or condensation polymer resin is prepared by interfacial reaction involving diacid chlorides or diisocyanates. The present invention does not utilize an interfacial polymerization to form the condensation polymer resin, thereby avoiding the use of toxic diacid chlorides and diisocyanates and avoiding the generation of undesireable byproducts associated with the interfacial condensation. Also, U.S. Pat. No. 4,797,339 discloses a toner comprising an inner layer of ion complex and an outer layer containing a flowability imparting agent; and U.S. Pat. No. 4,254,201 illustrates the use of pressure sensitive toner clusters or aggregates with each granule of the cluster or aggregate being comprised of a pressure sensitive adhesive substance encapsulated by coating film. Color pigment particles or magnetic particles can be present on the surfaces of the encapsulated granules to impart the desired color to the toners. Also, U.S. Pat. No. 4,727,011 discloses a process for preparing encapsulated toners which involves a shell forming interfacial polycondensation and a core forming free radical polymerization, and further U.S. Pat. No. 4,708,924 discloses the use of a mixture of two polymers, one having a glass transition temperature in the range of -90.degree. C. to 5.degree. C., and the other having a softening temperature in the range of 25.degree. C. to 180.degree. C. as the core binders for a pressure fixable encapsulated toner. Other prior art, all United States patents, are summarized below: U.S. Pat. No. 4,016,099, which discloses methods of forming encapsulated toner particles and wherein there are selected organic polymers including homopolymers and copolymers such as vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and the like, see column 6, beginning at line 3, wherein there can be selected as the core materials polyolefins, polytetrafluoroethylene, polyethylene oxide and the like, see column 3, beginning at around line 18; U.S. Pat. No. 4,265,994 directed to pressure fixable capsule toners with polyolefins, such as polytetrafluoroethylene, see for example column 3, beginning at line 15; U.S. Pat. No. 4,497,885, which discloses a pressure fixable microcapsule toner comprising a pressure fixable component, a magnetic material, and other optional components, and wherein the core material can contain a soft material, typical examples of which include polyvinylidenefluoride, polybutadiene, and the like, see column 3, beginning at line 10; U.S. Pat. No. 4,520,091, which discloses an encapsulated toner with a core which comprises a colorant, a dissolving solvent, a nondissolving liquid and a polymer, and may include additives such as fluorine containing resin, see column 10, beginning at line 27; U.S. Pat. No. 4,590,142 relating to capsule toners wherein additives such as polytetrafluoroethylenes are selected as lubricating components, see column 5, beginning at line 52; U.S. Pat. Nos. 4,520,091; 4,642,281; 4,761,358; 4,599,289 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent.
The disclosures of all the United States patents and other patent documents mentioned herein are totally incorporated herein by reference.
A number of United States patents and copending patent applications illustrate various encapsulated toner compositions and processes thereof, such as interfacial shell formation processes including, for example, U.S. Pat. No. 5,043,240, U.S. Pat. No. 5,035,970, U.S. Pat. No. 5,037,716 and U.S. Ser. No. 516,864, U.S. Pat. No. 5,045,253, U.S. Ser. No. 546,616, U.S. Ser. No. 456,278, U.S. Ser. No. 461,397, U.S. Pat. No. 5,082,757, U.S. Ser. No. 617,222, U.S. Pat. No. 5,023,159, U.S. Pat. No. 5,013,630, and U.S. Ser. No. 782,688, wherein there is disclosed, for example, a toner composition comprised of a homogeneous or substantially homogeneous mixture of polymer resin or resins, and color pigments, dyes, or mixtures thereof overcoated with a component derived from the condensation of a cellulose polymer with a silane component, the disclosures of each of the aforementioned copending applications and patents being totally incorporated herein by reference.